Within the field of solid-state color imagers, the production of a highly sensitive, high resolution, inexpensive imager is a well-recognized goal. In pursuit of this goal, a number of types of solid-state color imagers have been produced.
In one such imager, panchromatic image sensing elements in an array are selectively sensitized to color by means of an integral array of color filters disposed over the array of image sensing elements. Highly efficient configurations for such filter arrays that maximize the amount of usable image information, based on human visual acuity for color detail, have been described for example in U.S. Pat. No. 3,971,065 issued July 20, 1976 to Bayer, and U.S. Pat. No. 4,047,203 issued Sept. 6, 1977 to Dillon. However, the resolution capability inherent within such arrays is limited by the number of image sensing elements that can be placed on the array and are further limited in that only a portion of the elements in the array contribute to the resolution of fine detail. In addition, photosensitivity is limited in that only a portion of the array itself can be used as a photosensing area because the elements for each color are located at the same level as the other function of the device. Consequently, the special resolution of such integral filter color image sensing arrays, while optimized for the particular design, will not be as high as a monochrome image sensing array of the same number of elements. Furthermore, due to the shapes and patterns of filters utilized, and undesirable interference pattern referred to as moire occurs.
Moire is the spurious pattern which occurs in the reproduced picture resulting from interference beats between two sets of periodic structures in the image. Moires are produced, for example, by interference between the regular patterns in the original subject and the target grid in an image orthicon, between patterns in the subject and the line pattern and the pattern of phosphor dots of a three-color kinescope, and between any of the patterns and the pattern produced by the carrier color signal.
In order to increase sensitivity of the device, another structure has been proposed within U.K. Pat. No. 2,029,842 and Japanese Patent Application Laid Open (OPI) Nos. 55-39404; 55-27772; 55-2773; and 51-95720. The construction disclosed within these publications utilizes a photosensor superimposed on top of the information transfer device or MOS switching device. Due to the larger sensing area than is present with conventional imaging devices, where the photosensor is located on the same level as the information transfer device, the structure has significantly higher sensitivity. Due to the increased sensitivity obtained by utilizing a separate photosensor layer, this concept is utilized within the imager of the present invention. However, such structures utilize conventional filter shapes and patterns which result in moire interference as described above.
In an attempt to eliminate the moire interference problem as described above, a construction utilizing an offset arrangement of photosensing cells has been disclosed within Japanese Patent Application No. 50-128919. Another attempt to eliminate the moire pattern involves the production of an imager utilizing a one-dimensional offset pattern of the color filter array as disclosed within Japanese Patent Application No. 53-75728. Although the use of these offset patterns has some effect with respect to eliminating the moire interference, the interference is eliminated in only one dimension, i.e. in the vertical or horizontal dimension depending upon the manner in which the pattern is offset. Neither of the patterns is capable of eliminating the moire interference in both the vertical and horizontal dimensions.